A display apparatus can be equipped with or connected to one or more acoustic sensors and operation of the display apparatus can be made responsive to an audio signal detected by the one or more acoustic sensors. For example, publication U.S. Pat. No. 7,002,617 discloses a surveillance system that comprises a camera having a lens for viewing a 360 degrees field of view, a memory for storing visual data corresponding different sectors of the field of view, an acoustic sensor for detecting a direction of a location of a source of an audio signal, selection means for selecting visual data from the visual memory according to the detected direction of the location of the source of the audio signal, and a monitor for displaying the selected visual data. As another example, publication US2002003470 discloses an active gunshot warning system which uses acoustic sensors mounted on moving vehicles, fixed locations, or in combination with moving vehicles and fixed locations. The acoustic sensors are arranged to detect the occurrence of gunshots and to use audio information from the gunshots in combination with a blast library to identify the type of weapon or weapons used. Information related to the gunshots, detailing location, direction of movement, number of shots fired, and type of weapon or weapons can be forwarded in audiovisual form to police vehicles, or to the military where appropriate, to assist the authorities in their response to the gunshots.
The technical solutions of the kind described above are, however, unable to generate a visual marker or other visual indicator that would indicate a direction from which an audio signal having a limited temporal duration, e.g. a gunshot voice, has arrived with respect to a changing rotational position (orientation) of a display apparatus. One can consider, for example, a policeman or a soldier who has heard a gunshot and needs visual information that indicates the direction from which the voice of the gunshot has arrived also in a case in which the policeman or the soldier is changing the orientation of a display apparatus used by him.